Heat shielding structure for internal-combustion engines

Abstract

A plug boot contains an ignition cable which is fitted with the stud terminal of a spark plug extending from an engine cylinder block. This plug boot is covered with a heat shield, and further with an auxiliary heat shield. The cylinder-side end portion of the auxiliary heat shield is fixed between the spark plug and the cylinder block. The cable-side end portion of the auxiliary heat shield is provided with a lid unit. This lid unit includes a fixing retaining member and a pressing portion. The fixing retaining member fits the lid unit to the auxiliary heat shield, while the pressing portion exerts downward forces on the plug boot. By the combination of fitting forces and downward forces, the ignition cable and the spark plug are reliably connected.

What is claimed: 
     
       1. A heat shielding structure for internal-combustion engines including a cylinder block, said heat shielding structure connecting an ignition cable having a cable end to a spark plug, said heat shielding structure comprising: a spark plug including a stud terminal extending from said cylinder block;   a plug boot including a cylinder-side end portion and a cable-side end portion, said plug boot containing a high-voltage terminal held by pressure between said cable end and said stud terminal, so that said ignition cable and said spark plug are maintained in a connected state;   a heat shield having a substantially cylindrical shape and including a cylinder-side end portion and a cable-side end portion, said heat shield covering said plug boot;   an auxiliary heat shield including a cylinder-side end portion and a cable-side end portion, and covering said heat shield with a predetermined space therebetween; and   a lid unit including a pressing portion which contacts said cable-side end portion of said plug boot and a cable hole from which said ignition cable extends from said cable-side end portion of said plug boot;   whereby said cylinder-side end portion of said auxiliary heat shield is fixed between said spark plug and said cylinder block and said lid unit forms a locking arrangement together with said cable-side end portion of said auxiliary heat shield, whereby, when said lid unit is fitted to said cable-side end portion of said auxiliary heat shield, said pressing portion exerts a downward force on said plug boot through said locking arrangement.   
     
     
       2. The heat shielding structure according to claim 1, wherein said lid unit comprises a barrel portion which fits onto said cable-side end portion of said auxiliary heat shield and said locking arrangement comprises: a pair of recesses formed in said cable-side end portion of said auxiliary heat shield, at substantially diametrically distal positions thereof and in the tangential direction thereof;   a pair of notches formed in said barrel portion of said lid unit, at positions corresponding to those of said pair of recesses when said lid unit is fitted, said pair of notches including an opening; and   a U-shaped retaining member including a pair of grip portions;   wherein said U-shaped retaining member is fitted laterally into said notches, so that said pair of grip portions is exposed from said opening of said notches and wherein said lid unit is fitted onto said cable-side end portion of said auxiliary heat shield, so that said pair of grip portions is fitted into said pair of recesses.   
     
     
       3. The heat shielding structure according to claim 2, wherein said cable-side end portion of said heat shield is flared so as to be placed into contact with said lid unit, whereby said heat shield is grounded through said lid unit and said auxiliary heat shield. 
     
     
       4. The heat shielding structure according to claim 1, wherein said lid unit comprises a male portion which fits into said cable-side end portion of said auxiliary heat shield and said locking arrangement comprises: a pair of notches formed in said cable-side end portion of said auxiliary heat shield, at substantially diametrically distal positions thereof and in the tangential direction thereof, said pair of notches including an opening;   a pair of recesses formed in said male portion of said lid unit, at positions corresponding to those of said pair of notches when said lid unit is fitted; and   a U-shaped retaining member including a pair of grip portions;   wherein said U-shaped retaining member is fitted laterally into said notches, so that said pair of grip portions is exposed from said openings of said notches and wherein said lid unit is fitted onto said cable-side end portion of said auxiliary heat shield, so that said pair of grip portions is fitted into said pair of recesses.   
     
     
       5. The heat shielding structure according to claim 4, wherein said cable-side end portion of said heat shield is flared so as to be placed into contact with said lid unit, whereby said heat shield is grounded through said lid unit and said auxiliary heat shield. 
     
     
       6. The heat shielding structure according to claim 1, wherein said lid unit comprises a male portion which fits into said cable-side end portion of said auxiliary heat shield and said locking arrangement comprises: a plurality of shield ears protruding radially inwardly from said cable-side end portion of said auxiliary heat shield, said plurality of shield ears including first fixing members;   a plurality of lid ears protruding radially outwardly from said pressing portion of said lid unit, said lid ears including second fixing members;   wherein said lid unit is fitted into said cable-side end portion of said auxiliary heat shield while pressing down said plug boot by said pressing portion of said lid unit, such that said lid ears do not abut against said shield ears, and said lid unit is rotated, whereby said first fixing members are fitted with said second fixing members.   
     
     
       7. The heat shielding structure according to claim 6, wherein said cable-side end portion of said heat shield is flared so as to be placed into contact with said lid unit, whereby said heat shield is grounded through said lid unit and said auxiliary heat shield. 
     
     
       8. The heat shielding structure according to claim 6, wherein said shield ears each comprise an abutting member in a corresponding position thereof in a circumferential direction of said auxiliary heat shield, such that said lid ears abut against said abutting members at positions where said first fixing members and said second fixing members are to be fitted. 
     
     
       9. The heat shielding structure according to claim 8, wherein said cable-side end portion of said heat shield is flared so as to be placed into contact with said lid unit, whereby said heat shield is grounded through said lid unit and said auxiliary heat shield. 
     
     
       10. The heat shielding structure according to claim 1, wherein said locking arrangement comprises: a pair of flanges arranged at substantially diametrically distal positions of said auxiliary heat shield;   a pair of strips including a hook portion, a finger portion and a link portion serving as a fulcrum therefor, said pair of strips being arranged at positions corresponding to those of said pair of flanges when said lid unit is fitted, said pair of strips being connected to said lid unit through said link portion, such that said pair of strips can move in opposite directions and exert elastically restoring forces, wherein said pair of strips is fitted to said pair of flanges under said elastically restoring forces and said pair of strips is released from said pair of flanges by flexing said finger portions against said elastically restoring forces.   
     
     
       11. The heat shielding structure according to claim 10, wherein said cable-side end portion of said heat shield is flared so as to be placed into contact with said lid unit, whereby said heat shield is grounded through said lid unit and said auxiliary heat shield. 
     
     
       12. The heat shielding structure according to claim 1, wherein said lid unit comprises a barrel portion which fits onto said cable-side end portion of said auxiliary heat shield, said barrel portion including a circular bottom rim, a plurality of slits extending onwardly therefrom, and an inner circular face, and said locking arrangement comprises: a flared portion provided in said cable-side top portion of said heat shield;   first fixing members provided in said cable-side top portion of said auxiliary heat shield;   a plurality of slats, formed in said barrel portion and defined by said plurality of slits; and   second fixing members provided on said plurality of slats;   wherein, when said lid unit is mounted onto said cable-side end portion of said auxiliary heat shield, said flared portion of said heat shield abuts against said inner circular face of barrel portion, and said first fixing members fit with said second fixing members.   
     
     
       13. The heat shielding structure according to claim 12, wherein said cable-side end portion of said heat shield is flared so as to be placed into contact with said lid unit, whereby said heat shield is grounded through said lid unit and said auxiliary heat shield. 
     
     
       14. The heat shielding structure according to claim 1, wherein said lid unit comprises a male portion which fits into said cable-side end portion of said auxiliary heat shield and said locking arrangement comprises: a plurality of contact sections which contact said auxiliary heat shield when said lid unit is fitted, said contact sections including first fixing members;   a plurality of recessed sections arranged so as to alternate with said contact sections, said recessed sections not being in contact with said auxiliary heat shield; and   second fixing members provided in said cable-side end portion of said auxiliary heat shield, said second fixing members being arranged at the positions corresponding to those of said first fixing members when said lid unit is fitted;   wherein said male portion is fitted into said auxiliary heat shield, such that said second fixing members are led through said recessed sections, and said lid unit is rotated, so that said first fixing members and said second fixing members are fitted together.   
     
     
       15. The heat shielding structure according to claim 14, wherein said cable-side end portion of said heat shield is flared so as to be placed into contact with said lid unit, whereby said heat shield is grounded through said lid unit and said auxiliary heat shield. 
     
     
       16. The heat shielding structure according to claim 1, wherein said cable-side end portion of said heat shield is flared so as to be placed into contact with said lid unit, whereby said heat shield is grounded through said lid unit and said auxiliary heat shield. 
     
     
       17. The heat shielding structure according to claim 1, wherein said lid unit is provided with air-ventilation holes. 
     
     
       18. The heat shielding structure according to claim 1, wherein said cylinder-side end portion of at least one of said auxiliary heat shield and said heat shield is provided with water drainage holes. 
     
     
       19. A heat shielding structure for internal-combustion engines including a cylinder block, said heat shielding structure connecting an ignition cable having a cable end to a spark plug, said heat shielding structure comprising: a spark plug including a stud terminal extending from said cylinder block;   a plug boot including a cylinder-side end portion and a cable-side end portion, said plug boot containing a high-voltage terminal held under pressure between said cable end and said stud terminal, so that said ignition cable and said spark plug are maintained in a connected state;   a heat shield having a substantially cylindrical form and including a cylinder-side end portion and a cable-side end portion, said heat shield covering said plug boot;   an auxiliary heat shield including a cylinder-side end portion and a cable-side end portion, and covering said heat shield with a predetermined space therebetween; and   a lid unit including a pressing portion which contacts said cable-side end portion of said plug boot and a cable hole from which said ignition cable extends from said cable-side end portion of said plug boot;   whereby said cylinder-side end portion of said heat shield is fixed between said spark plug and said cylinder block and said lid unit forms a locking arrangement together with said cable-side end portion of said auxiliary heat shield, whereby, when said lid unit is fitted to said cable-side end portion of said auxiliary heat shield, said pressing portion exerts a downward force on said plug boot through said locking arrangement, and wherein said heat shield and said auxiliary heat shield are integrally formed through each of said cable-side end portions thereof.   
     
     
       20. The heat shielding structure according to claim 19, wherein said cable-side end portion of said heat shield is flared so as to be placed into contact with said lid unit, whereby said heat shield is grounded through said lid unit and said auxiliary heat shield.